Fast Fret has been in existence for 40 years and is very popular, particularly with guitarists. It’s not a spray. It’s a block on a stick which is applied to your strings and fingerboard to remove built up dirt and grime. Fast Fret keeps the strings sounding bright and new, extending the healthy lifetime of any strings. According to the official blurb Fast-Fret allows you to play faster, maintains brightness, prolongs the life of your fingerboard wood - and it's effects are long lasting.
“I bought a tin of this is 1981 and I still have it! It still works as well!”